1. Technical Field
The present invention relates to an electronically controlled hydraulic actuation type fuel injection device adapted to be used in a diesel engine and an oil viscosity detection device and method utilized in the fuel injection device.
2. Background Art
Conventionally, an electronically controlled hydraulic actuation type fuel injection device as described in WO 93/07381 has been known as a typical fuel injection device adapted for use in a diesel engine. In such a device, relatively high pressure hydraulic oil is supplied to each unit injector for operating a pressure intensifying piston inside the unit injector with the working hydraulic pressure such that the pressure intensifying piston pressurizes relatively low pressure fuel reservoired inside the unit injector to the injection pressure and the pressurized fuel lifts up a needle valve for carrying out fuel injection. It should be noted that lubricating oil for lubricating the engine is used as the hydraulic oil in such devices as above.
Hydraulic pressure supplied to the pressure intensifying piston is controlled by opening/closing a solenoid valve integrated into the unit injector by way of a controller such as ECU. Signals indicative of engine speed, accelerator opening, crank angle etc. are input in the controller. The controller determines valve opening time during which the solenoid valve to be kept open based on the engine speed and the accelerator opening data, utilizing a pre-memorized map. The controller then sets the solenoid valve in on-state only during the determined (valve opening) time, allowing an adequate hydraulic pressure to be supplied to the pressure increasing piston to carry out fuel injection of a level that is appropriate for the current operational state of the engine. The controller also controls the oil manifold internal pressure as pressure reservoir in accordance with the operational state of the engine such that the working hydraulic pressure supplied to the solenoid valve can be controlled.
In the conventional fuel injector of the structure described above, the amount of fuel injection is determined according to the time during which the solenoid valve to be kept open. However, this system has a defect that the amount of fuel injection per time (time during which the solenoid valve is kept open) may vary in accordance with the change in viscosity of the working hydraulic oil. Hydraulic oil (lubricating oil for the engine is used as hydraulic oil) inevitably experiences change in its viscosity according to the use grade, temperature, deterioration state and the like. Since resistance the hydraulic oil experiences as it passes through the solenoid valve varies according to such change in viscosity, the flow amount of the hydraulic oil per time (time during which the solenoid valve is kept open) also varies. If the flow amount of the hydraulic oil per time changes, the operational state of the pressure intensifying piston and the needle valve cannot be kept constant, resulting in variation of the amount of fuel injection. The variation of injected fuel amount may cause lower engine power, increased emission of harmful products such as smoke in the exhaust gas.